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The utilization of alkali metal anodes is hindered by an inherent instability in organic electrolytes. Sodium is of growing interest due to its high natural abundance, but the carbonate electrolytes popular in lithium systems cannot form a stable solid electrolyte interphase (SEI) with a sodium electrode. Using half-cell and symmetric-cell analysis, we identify specific glyme (chain ether) electrolytes that produce thin, predominantly inorganic SEI at the sodium metal interface, and we study the effect of ethylene carbonate and fluoroethylene carbonate (FEC) additives on the SEI formed in these systems via X-ray photoelectron spectroscopy. Through in situ optical microscopy, we observe the onset and growth of sodium dendrites in these electrolytes. We determine that the SEI formed by glyme alone may not support extensive or extreme cycling conditions, but the addition of FEC provides a more robust SEI to facilitate numerous consistent sodium plating and stripping cycles.
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The Impact of Fluoroethylene Carbonate Additive on Charged Sodium Ion Electrodes/Electrolyte Reactivity Studied Using Accelerating Rate Calorimetry
The effects of fluoroethylene carbonate (FEC) electrolyte additive on charged sodium ion electrode/electrolyte reactivity at elevated temperatures were investigated using accelerating rate calorimetry (ARC). The beneficial effect of FEC on cell lifetime was demonstrated using Na0.97Ca0.03[Mn0.39Fe0.31Ni0.22Zn0.08]O2(NCMFNZO)/hard carbon (HC) pouch cells first prior to ARC measurements. Electrodes from these pouch cells were utilized as sample materials and 1.0 M NaPF6in propylene carbonate (PC):ethyl methyl carbonate (EMC) (1:1 by vol.) was chosen as control electrolyte. Adding 2 wt% and 5 wt% FEC to the electrolyte does not significantly affect the reactivity of de-sodiated NCMFNZO compared to the control electrolyte. However, the addition of FEC obviously changed the reactivity between sodiated HC and electrolytes, especially by showing a suppression on the exothermal behavior between 160 °C and 230 °C. These results give a head to head comparison of the reactivity of FEC additive containing electrolytes with charged sodium ion electrode materials at elevated temperatures and show that the use of FEC at additive levels should not compromise the cell safety when extending cell lifetime.
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- Award ID(s):
- 2301719
- PAR ID:
- 10472161
- Publisher / Repository:
- The Electrochemical Society
- Date Published:
- Journal Name:
- Journal of The Electrochemical Society
- Volume:
- 170
- Issue:
- 11
- ISSN:
- 0013-4651
- Format(s):
- Medium: X Size: Article No. 110501
- Size(s):
- Article No. 110501
- Sponsoring Org:
- National Science Foundation
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